Initially, pure copper wires were used as wire electrodes, which copper wires have been replaced with brass wires having a greater mechanical tensile strength. Compared with the pure brass electrode, a wire electrode which is provided with a coating has proven to be advantageous, in particular a coating of a material which has a low evaporation temperature. Such a wire electrode has become known from German Offenlegungsschrift No. 29 06 245. Particularly advantageous is a coating of zinc which, in the sequence of elements which are organized according to their evaporation points, is the first metal free of corresponding difficulties in use, which result for example from too great a chemical reactivity or toxicity. This metal wears off easily or erodes easily, but this is not a disadvantage because, during spark-erosive wire cutting, the wire part used is continuously renewed.
The brass-wire electrodes which are coated with zinc have brought about a considerable increase in cutting performance, but these brass-wire electrodes still have the disadvantage that, during final annealing of the wire to adjust same to the needed solidity, a portion of the zinc diffuses into the brass core, which necessitates increased energy for setting free the zinc which is needed for the eroding action.
A basic purpose of the invention is to provide a wire electrode which has, compared with the known brass-wire electrode coated with a zinc layer, a substantially increased cutting performance and in which the diffusing of the zinc into the wire core is substantially reduced.